1. Field of the Invention
The present invention concerns clamps and workpiece holders. More particularly, it concerns a means of securely clamping a sine plate. Sine plates are used to accurately locate a workpiece at an ultra precision chosen angle. They usually comprise two pivoting plates hinged on a mutual edge. A gage block or combination of gage blocks is set between the spread apart plates to hold them to a particular angular relationship.
Usually these gage blocks are held in place by a locking strap attached to the side of the sine plate. Sine plates are often set at a steep angle (i.e., large angle between the top and bottom plates). Many times the weight is on the outside center pivot of the sine plate hinge, putting it off balance and causing to fall open, thus throwing the part being machined into the grinding wheel or machining cutter. Sine plates are usually stable when the angle between the top and bottom plates is shallow.
It is a common practice to put screws into holes on the open end of the sine plate and to use rubber bands looped around the screws and the workpiece to prevent any movement. This is a very insecure means of holding the workpiece in position. The stacks of blocks are prone to vibrate loose in the machining process. Forces present during machining of a workpiece mounted onto the sine plate can vibrate the gage blocks loose and collapse the sine plate and the workpiece. Such a collapse can present danger and possible injury to the worker involved with the workpiece.
Presented in this application is a new and effective means of securely clamping a sine plate in position.
2. Description of the Prior Art
Numerous previously disclosed devices have made use of the screw tightened tension of a flexible member in order to tighten a clamp hold. Some of these devices known to the applicant are listed and discussed below.
U.S. Pat. Nos. 1,227,449 and 2,903,930 issued to Jones and Peterson et al. respectively disclose pipe vises with chain-tightening screw wherein the chain encircles the pipe disposed on the vise cradle.
U.S. Pat. No. 826,131 issued to weaver describes an adjustable screw bolt that acts as a tension clamp. The force that is applied is purely linear, as the direction of tension is in line with the axis of the bolt.
U.S. Pat. No. 2,583,917 issued to Wiegant describes a chain clamp use to hold a workpiece while a lathe cuts a slot or keyway into the workpiece.
U.S. Pat. Nos. 1,326,999, 1,410,553 and 2,968,978 issued to Wallace et al., Cox and Wheeler disclose similar pipe clamps that make use of wrap around chains which are tensioned by means of a screw bolt attached to one end of the chain. None of the above recited clamp devices are used with a sine plate. The above devices are concerned with the holding steady of an object and not its exact positioning.
U.S. Pat. No. 4,398,349 issued to Bailey shows an arctuate locking strap having one end pivotally mounted to the base of a sine plate. The arctuate section of the strap has a slot in which rides a clamping bolt threaded into the top plate, for fixing the strap to the top plate in a certain position and thereby fixing the angle of the top plate. The arc of the strap is of varying radius such that the strap never rides above the edge of the top plate.